Mouse Study Sheds New Light on How Memories Are Stored

During sleep, and even under anesthesia, part of the brain behaves as if it's remembering something, new animal research suggests.

The finding about the entorhinal cortex -- which is involved in learning, memory and Alzheimer's disease in humans -- challenges conventional theories about memory consolidation during sleep, the University of California, Los Angeles researchers said.

For the study, which was performed on mice, the researchers measured the activity of single neurons from three parts of the brain involved in memory formation in order to identify which brain region was activating other areas of the brain and how this activation was spreading.

The investigators discovered that the entorhinal cortex has what is called persistent activity, which is believed to be involved in working memory when people are awake, such as remembering a phone number or following directions.

"The big surprise here is that this kind of persistent activity is happening during sleep, pretty much all the time," study senior author Mayank Mehta, a professor of neurophysics, said in a UCLA news release. "These results are entirely novel and surprising. In fact, this working memory-like persistent activity occurred in the entorhinal cortex even under anesthesia."

Persistent activity in the entorhinal cortex during sleep may be a way to unclutter memories and delete information that was processed during the day but not needed, which results in important memories becoming prominent and readily accessible, Mehta suggested.

The findings are important because people spend one-third of their lives sleeping, and a lack of sleep causes various health problems, including learning and memory problems, Mehta said. The researcher also noted that Alzheimer's disease starts in the entorhinal cortex and these patients are known to have sleep problems.

However, experts point out that results from animal research are not necessarily applicable to humans.

The study was published online Oct. 7 in the journal Nature Neuroscience.